The main focus is to understant eh cellular, molecular and biochemical bases for radioresistance and radiation-induced changes in cell cycle progression. The proposed investigations would use the soft neutrons as a DNA damaging agent to study cell survival and the induction of a cell cycle delay (checkpoint) response in wild-type cells. Once condtions are established such that the delay can be detected, these studies will also be conducted in S. Pombe mutants known to be defective in checkpoint control caused by exposure to UV light or gamma-rays, previously tested radiations. This study will identify the genetic elements that mediate low energy neutron-mediated cell killing and alterations in cell cycle progression. The timing of the delay in synchronized populations and the dose response, in relation to cycling delay and cell survival, will also be determined to further characterize soft neutron-mediated changes in cell cycle progression. An important reason to use the low-energy neutrons is their relevance as an occupational hazard to airline and nuclear power workers. This study will serve to better characterize the biological response to this type of radiation.